Wilson, Robert W. (1936- )

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Wilson, Robert W. (1936- )

American physicist

Robert Woodrow Wilson is best known for the discovery, with co-researcher Arno Penzias , of the cosmic background radiation believed to be the remnant of the "big bang" that started the Universe. For their work, Wilson and Penzias were honored with numerous awards, including the 1978 Nobel Prize in physics, which they shared with Pyotr Kapitsa.

Wilson was born in Houston, Texas. He attended Rice University where he received a B.A. in physics in 1957. He then moved on to the California Institute of Technology (Cal Tech) for graduate study and received his Ph.D. in 1962. Wilson's thesis work and post-doctoral research involved making radio surveys (the use of radio waves bounced off of stellar bodies to create visual approximations) of the Milky Way Galaxy. When he heard of the existence of specialized radio equipment at Bell Laboratories, he left Cal Tech and accepted a job at Bell's research facility in Holmdel, New Jersey. This was the very same research facility from which Karl Jansky , in the 1930s, almost single-handedly invented the science of radio astronomy . Wilson and Penzias, who had preceded Wilson at Bell Labs by about a year, were about to embark on a research odyssey that would culminate in an extremely important discovery almost by accident.

Just as Jansky had done thirty years earlier, Wilson and Penzias were studying the possible causes of static interference that impaired the quality of radio communications. At least, this was what the management at Bell hoped would transpire as the two radio astronomers conducted their research. Wilson and Penzias' long-range plan was to measure radiation in the galactic "halo," a theorized but not well understood cloud of matter and radiation surrounding the Milky Way and other galaxies. Then, they hoped to look for hydrogen gas in clusters of galaxies. Their research instrumentation included a small, sensitive 20-foot microwave "horn" originally designed to receive bounced radio reflections from the Echo communications satellite .

Because galactic radio radiation is, by its nature, not very energetic, the central problem in measuring its precise intensity was to eliminate all conceivable sources of heat, or thermal noise, which could obscure an accurate reading of the weak radio signals from space . To this end, Penzias had laboriously constructed a "cold load," using frigid liquid helium, which would cool the radio detector down to within only a few degrees above absolute zero. When the equipment was finally ready in the spring of 1964, the radio horn was turned to the sky.

Very early in the research project, it became apparent that the antenna was measuring more radio radiation than Wilson and Penzias had anticipated. The source of the excess radiation could not be determined. A similar problem had surfaced earlier when the twenty-foot horn was used for Echo satellite communications. At that time, researchers added up all the known sources of accounted radio noise, which totaled a heat measurement of 19 degrees Kelvin. It was therefore puzzling to them that the radio receiver was measuring 22 degrees. Wilson and Penzias' results were similar. They had hoped that their carefully modified apparatus would yield more accurate results, but this apparently was not the case. They were measuring a significant amount of excess microwave radiation. The intensity of the signal did not change regardless of where they pointed the receiver. Nor did the radio static appear to be coming from any discrete object in space. The Milky Way Galaxy was not the source either, since the radio signal seemed to be coming from everywhere in the universe at once, not from just a limited zone across the sky. Based on the known sources of radio radiation, the strength of this radiation was far more powerful than expected.

Wilson and Penzias checked for possible explanations for this phenomenon, concluding that atmospheric effects were not to blame. Since the hill upon which their radio horn was perched overlooked New York City, the possibility of interference from man-made sources was considered. After repeated observations, however, Wilson and Penzias were convinced that New York was not to blame. To insure that the signal was not the result of interference from their own electronic apparatus, Wilson and Penzias tracked down and eliminated every conceivable source of noiseincluding the effects of bird dung, which coated the inside of the radio horn, courtesy of a pair of nesting pigeons. The interior of the radio horn was cleaned out.

The attempts to improve the performance of the radio horn took time. Finally, in 1965, the antenna was re-activated and careful observations were made of the radio flux from the sky. The results revealed that the telescope was performing better than ever, but the mysterious excess signal remained. The intensity of the excess radio noise was what would be expected from an object, or source, with a very low temperatureonly a few degrees above absolute zero. In this case, as with the previous observation, the static was not coming from a discrete source but was emanating uniformly from every direction in the sky.

While Wilson and Penzias were trying to make sense of what seemed to them to be a failed experiment, Robert Dicke and his colleagues at Princeton University, unaware of the project at Bell Labs, were building a radio receiver of their own designed to look for the very radiation that Wilson and Penzias had unintentionally observed. Whereas Wilson and Penzias had rather modest hopes of making simple surveys of galactic radio flux, Dicke was looking for physical evidence of the creation of the universe. Dicke had been researching the theoretical effects of the big bang, the expanding fireball theorized as the birth of the Universe.

The line of reasoning Dicke followed was that as the universe expanded after the big bang, gases cooled and thinned but were still dense enough to block electromagnetic radiation. All thermal energy released by atoms, including light and heat, was reabsorbed by other atoms in the gas almost instantly. One consequence of this condition was that if someone could have viewed the universe from the "outside" at this point, they would have seen only blackness, since no light could escape the opaque, light-absorbing gas. Eventually, there must have come a time, thousands of years after the big bang, when the average density of the expanding universe was finally low enough to allow heat and light to escape from atoms unimpeded, much as the light and heat generated in the sun's interior eventually escapes through the sun's transparent photosphere. According to the theory that Dicke was exploring, the rapid release of newly freed energy in the thinning, early universe would have taken the form of an incredibly sudden blaze of heat and light, almost like an explosion.

How could this "primeval fireball," as it came to be called, be observed today? If the remnant of this energy flash had survived after several billion years, it would be detected as a kind of "whisper" in a radio telescope. It would have a specific color and temperature and would be present in nearly equal intensities in every direction, forming a cosmic background radiation. This radiation would flood every available volume of space. In time, the radiation would appear to cool down to a point near absolute zero, due to the further expansion of the universe, but it would still be detectable even in the present-day universe. It was precisely this radiation that Robert Dicke was preparing to look for with his own radio telescope. It was also this radiation, measuring close to absolute zero (around 3 Kelvin) in uniformity across the sky, that Wilson and Penzias had already discovered.

Wilson and Penzias were not cosmologists, however. They could not explain their observation of the microwave radiation at the 7.3 cm wavelength, and so they contacted Dicke, who they knew was working on this problem. When Dicke heard the details of their findings, he knew that Wilson and Penzias had discovered exactly what he was looking for; the cold, background radiation left over from the big bang. In 1965, Wilson and Penzias published their results in a paper entitled "A Measurement of Excess Antenna Temperature at 4,080 Mc/s." A companion paper written by Dicke, P.J.E. Peebles, P.G. Roll, and D.T. Wilkinson explained the profound cosmological implications of the finding.

The discovery of the cosmic background radiation was like finding the intact skeleton of a dinosaur. The radiation is a "fossil," an ancient relic from a time when the universe was barely 100,000 years old. The discovery of the radiation was to become the second great pillar upon which the big bang theory would rest, second only to the 1920s discovery of the expansion of the universe. The fact that the background radiation was predicted in advance of its discovery helped to strengthen the big bang theory, so much so that most competing theories about the birth of the universe, such as steady state, almost immediately fell away after 1965.

As scientists around the world began making their own confirming observations of the cosmic background radiation, it became apparent to those searching past research papers that clues to the existence of the radiation had existed for over 25 years. The most striking example came from 1938, in which optical telescopic observations revealed that interstellar cyanogen gas was being heated, unaccountably, by a 3-degree source. This source was nothing less than the cosmic background radiation. But at the time, no one imagined that the seemingly innocuous source of heat could be the remnants of the big bang fireball. It would not be until Wilson and Penzias's discovery that the cosmic radiation would be identified for what it was.

Wilson and Penzias's discovery was acclaimed by scientists around the world. In 1976, Wilson was named head of the Radio-Physics department of Bell Telephone. For his work on the cosmic background radiation, he also received the Henry Draper Award, in 1977, from the National Academy of Sciences. In 1978, the importance of their achievement in the history of science was fully recognized when Wilson and Penzias shared the Nobel Prize in physics with Kapitsa.

See also Cosmic microwave background radiation